Several TBC GAP family members, e.g., TBC1D3, TBC1D7, TBC1D8, TBC1D10A, TBC1D16, TBC1D17, TBC1D23, EVI5, TRE2, and RN‐TRE, have been implicated in various types of cancer through their Rab‐GAP activity or GAP‐independent signaling.[16, 32, 33, 34, 35, 36, 37, 38, 39] As an uncharacterized member of the TBC GAP family, TBC1D31 has recently been found to be a molecular scaffold for assembling OFD1, praja2 and PKA, and plays an important regulatory role in cilium biogenesis.[40] However, its tumorigenic role remains unknown, especially its effect in modulating the GTPase signaling. Here, TBC1D1 is linked to cancer.